goals: define a polygon define and use reflectional symmetry and rotational symmetry
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Polygons and Symmetry. Goals: Define a Polygon Define and Use reflectional symmetry and rotational symmetry Define regular polygon and use the central angle theorem of a regular polygon. Examples. Not Polygons. Polygons. Vocab. - PowerPoint PPT PresentationTRANSCRIPT
Goals:•Define a Polygon
•Define and Use reflectional symmetry and rotational symmetry
•Define regular polygon and use the central angle theorem of a regular polygon
POLYGONS AND SYMMETRY
EXAMPLES
Polygons Not Polygons
VOCABTerm Picture Definition
Polygon
Sides of a Polygon
Vertices of a Polygon
Segments of a polygon
A closed plane figure formed by three or more segments such that each intersect exactly two other segments.
The common endpoints of those segments
Term Picture Definition
Equiangular Polygon
Equilateral Polygon
Regular Polygon
Central Angle
All angles congruent
All sides are congruent
Both equiangular and equilateral
An angle whose vertex is the center of the polygon and whose sides pass through two consecutive vertices
POLYGONS CLASSIFIED BY NUMBER OF SIDES
# sides Name of Polygon
# sides Name of Polygon
3 triangle 9 nonagon
4 quadrilateral 10 decagon
5 pentagon 11 11-gon or hendecagon
6 hexagon 12 dodecagon
7 heptagon 13 13-gon
8 octagon n n-gon
Reflectional Symmetry: A figure has reflectional symmetry if and only if
its reflected image across a line coincides exactly with the preimage, the original figure.
Axis of Symmetry: A line that divides a figure into two congruent reflected halves.
DRAW ALL AXES OF SYMMETRY ON EACH FIGURE
Rotational Symmetry: A figure has rotational symmetry if and only
if it has at least one rotation image not counting rotation images of 0º or multiples of 360º, that coincide with the original figure.
HOW MANY TIMES DOES EACH FIGURE HAVE ROTATIONAL SYMMETRY?
ACTIVITY WITH PATTY PAPER…
The measure of a central angle of a regular polygon with n sides is given by the following formula:
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EXAMPLE 1: FIND THE MEASURE OF THE CENTRAL ANGLE OF EACH REGULAR POLYGON BELOW:
a) decagon b) heptagon c) 15-gon
Measure of central angle: Measure of central angle: Measure of central angle: